Gem faceter

ABSTRACT

A gem faceter comprising a pivot block which is vertically movable to various positions, a pivot arm pivotally mounted at one end to the pivot block, a head mounted to the other end of the pivot arm and adapted for movement to various positions about a pivot pin, a dop mounted in said head and adapted to be rotated about its axis to various positions, an index plate fixedly mounted on said dop and having markings thereon which indicate the number and position of desired facets to be ground on a gem held by the dop, an index plate clamp for locking the index plate successively in said desired marked positions relative to the head for grinding the desired facets, a lapping table adapted to be contacted by the dopped gem, a protractor for continuously indicating the angular position of the dop relative to the vertical, an adjustable stop for limiting the movement of the head toward the lapping table, a sensor mounted on the stop for sensing the degree of movement of the head toward the lapping table, an electronic circuit for translating the degree of movement sensed by the sensor into an electronic signal, and a visual indicator for indicating the value of the electronic signal and the degree of said movement, whereby the faceting angle may be detected and duplicated with great precision.

[451 May 21, 1974 1 1 GEM FACETER [75] Inventor: Earl D. Montgomery,Warrington,

[73] Assignee: The American Standard Corporation, T'revose, Pa.

[22] Filed: Mar. 5, 1973 [21] Appl. No.: 338,406

[52] US. Cl 51/125, 51/216 LD [51] Int. Cl B24b 7/22, B24b 9/16 [58]Field of Search 51/71, 109 R, 125, 125 S,

51/122, 134.5 R, 216 L, 216 D, 216 H, 216

[56] References Cited UNITED STATES'PATENTS 1,214,009 1/1917 Coleman...51/125 1,520,948 12/1924 Heinz 51/125 1,730,767 10/1929 Havlicek 51/2292,829,472 4/1958 Salzer 51/125 3,098,327 7/1963 Malin l 51/125 3,110,13611/1963 Spira 51/125 3,439,456 4/1969 Bailey 51/125 3,520,088 7/1970Leibowitz 51/122 Primary Examiner-Othell M. Simpson v Attorney, Agent,or FirmSmith, Harding, Earley & Follmer [5 7 ABSTRACT A gem facetercomprising a pivot block which is vertically movable to variouspositions, a pivot arm pivotally mounted at one end to the pivot block,a head mounted to the other end of the pivot arm and adapted formovement to various positions about a pivot pin, a dop mounted in saidhead and adapted to be rotated about its axis to various positions, anindex plate fixedly mounted on said dop and having markings thereonwhich indicate the number and position of desired facets to be ground ona gem held by the dop, an index plate clamp for locking the index platesuccessively in said desired marked positions relative to the headforgrinding the desired facets, a lapping table adapted to be contactedby the dopped gem, a protractor for continuously indicating the angularposition of the dop relative to the vertical, an adjustable stop forlimiting the movement of the head toward the lapping table, a sensormounted on the stop for sensing the degree of movement of the headtoward the lapping table, an electronic circuit for translating thedegree of movement sensed by the sensor into an electronic signal, and avisual indicator for indicating the value of the electronic signal andthe degree of said movement, whereby the faceting angle may be detectedand duplicated with great precision.

10 Claims, 7 Drawing Figures PATENTED KAY 9 SHEET 3 0F 3 GEM FACETERBACKGROUND OF THE INVENTION This invention relates to grinding andpolishing machines, and more particularly is concerned with machines forgrinding facets on gem stones.

Conventional gem faceters are large, complicated pieces of machinerywhich are difficult to operate, especially by an amateur who is grindingfacets on semiprecious gems as a hobby. While all such machines mountthe gem to be faceted onto a dop, it is difficult for an operator toposition the dop for the desired number and position of facets, and itis difficult for the operator to align adjacent facets, such aspavilion, girdle, and crown facets. Some such machines do not providefor positioning the dop vertically in a first head to grind the table ofa gem, and require that the dop be removed from the first head and thenplaced and positioned precisely in an adapter head to grind the table.

In some of the prior art faceting machines, the dop is mounted in aquill rotatably mounted in a head which is pivotally mounted about ahorizontal shaft so as to permit the gem mounted on the bottom of thedop to be moved in a vertical plane and brought into contact with thelapping table. For facet angles which are small with respect to the gemtable, the grinding operation becomes increasingly difficult as thepivot pin of the head is moved upwardly and father away from the lappingtable.

Prior art faceters included a large number of structural members, andthose members were required to be of large size in order to'maintain thestructural rigidity that is necessary if good repeatability of facets isto be achieved, since there was a tendency for the structural members toflex under the strain of lap drag.

It was also difficult in prior machines to maintain the mounting post invertical alignment because this post was moved back and forth in amounting groove for various facet angles. Grit and debris couldaccumulate in this mounting groove to cause small but importantdeviations in the vertical alignment of the post and facet angles.

Another disadvantage of a number of the prior art machines was that thedop-quill-head assembly tended to become fairly heavy so that theoperator had to be very careful when placing the stone onto the lap inorder to avoid damaging the stone or breaking it away from the dop.Another disadvantage was that the size and mass of the prior artmachines increased their cost.

SUMMARY OF THE INVENTION It is an object of this invention to overcomethe disadvantages of the prior art and provide a gem faceter of greaterstability, of smaller size, and with fewer components than the prior artmachines, and which is simpler,

- position relative to pivot arm 33 by a head clamp knob easier to use,and less costly. Other objects include pro- BRIEF DESCRIPTION OF THEDRAWINGS FIG. 1 is a view in side elevation of a gem faceter constructedin accordance with this invention;

FIG.2 is a view in top plan of the gem faceter of FIG.

FIG. 3 is a left end view in elevation of the gem faceter of FIG. 1;

FIG. 4 is a view in elevation on an enlarged scale of the micrometerwhich forms an element of the invention, taken as indicated by thecircle indicated by the arrow 4 in FIG. 1;

FIG. 5 is a view in side elevation of the micrometer apparatus of FIG.4;

FIG. 6 is a view in top plan of the micrometer apparatus of FIG. 5; and

FIG. 7 is a diagrammatic view of the electrical circuit of themicrometer apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to the specificembodiment of the invention shown in the drawings, there is shown a gemfaceter 11 which comprises a base 13 that rotatably supports ahorizontal lapping table 15 positioned in a splash pan 17 made of aflexible rubber material and driven by a motor 19. A vertical post 21 isthreaded through base 13, and may be moved vertically relative to base13 by turning vertical adjustment knob 23 to thread post 21 through locknut 25 which locks post 21 in desired'vertical position. Nut 25- bearsagainst a mount 27 which rests on the top of base 13.

The top of post 21 is unthreaded and is received by hole 28 in a pivotblock 29 which may be moved in a horizontal plane around post 21 as apivot. Accordingly, pivot block 29 may be positioned at a desiredvertical position by turning vertical adjustment knob 23 to move post 21vertically, and' pivot block 29 may be positioned horizontally byrotating it to a desired position around post 21.

A pivot-block pulley 31 is fixedly mounted on pivot block 29. One end ofa pivot arm 33 is pivotally mounted on pivot block, 29 by a shaft or pin37 having one end threaded into a nut 39 and the other end clamped by agirdle block 41 separated from pivot block 29 by a spacer 43. Screw 45clamps the girdle block 41 onto shaft 37 by closing slot 47 to bringpor- 1 tion 49 of girdle block 41 to bear against shaft 37.

A head 51 is pivotally mounted on the other end of pivot arm 33 by ashaft or pin 53. Head 51 is locked in 55 which screws into a threadedhole in shaft 53.

A head pulley 57 is freely mounted on shaft 53 and is connected to blockpulley 31 by an endless cable or timing belt 59. A protractor 61 isfixedly mounted on head pulley 57, and has markings indicating anglesfrom 0 at top vertical marking 63 to at the horizontal marking. An angleindicator or pointer 65 extends from head 51 in alignment with the axisof a dop 67 mounted on head 51. Accordingly, a dop 67 is inserted .intohead 51 and clamped therein by turning head clamp handle 69 of headclamp 70, stone 71 mounted on dop 67 is placed on the lap 15, the dop 67is rotated about shaft 53 until the pointer 65 indicates the desiredcutting angle, 42 for example, and the head 51 is clamped in place onshaft 53 by turning head clamp knob 55. The pointer 65 indicates theangular position of the dop axis relative to the vertical.

A programmed index plate 72 is fixedly mounted on dop 67 and is providedwith notches 73 at predetermined and desired positions along itsperiphery to indicate the position and number of facets to be groundinto the stone or gem 71. An index plate clamp 75 is mounted above head51 and includes a finger 77 which is spring-loaded upwardly and isadapted to seat in the notches 73 to hold index plate 72 and dop 67 fromrotation during the grinding of a facet. Finger 77 is locked in notches73 against the spring force by the downward pressure from a lockingscrew 79.

in a conventional index plate, the notches are spaced evenly around itsperiphery and are numbered sequentially, for example, from 1 to 64 forastandard 64 posi-.

tion index plate. To cut a series of facets, the operator must selectthe notches by number and only these notches which are required for hisspecific type of cut. Instead of the conventional numbered notches,index plate 72 is programmed with just the notches needed for cuttingthe desired shape of stone. For example, the illustrated index plate 72is programmed for cutting ovals. The notches are not numbered and arenot spaced apart a uniform distance. Other index plates are programmedfor cutting other desired gem shapes, such as oval brilliant, or marqui.

' The degree of angular movement of the pivot arm 33 about pin 37, andalso the degree of angular movement about pin 37 of dop 67 and head 51,which are clamped to pivot arm 33 by head clamp knob 55, is limited by Va stop member 91 which extends from pivot block 29 and" supports abracket 93 having a sensor 95 mounted thereon. A stop adjustment screw97 is adapted to contact pivoted upper plate 95a of sensor 95 to move ittoward fixed lower plate 95b and signal an electrical circuit includinganamplifier and a meter indicator which is hereinafter explained. Screw97 is adjustably mounted by being threaded into a rod 99 extending frompivot arm 33. If desired, sensor 95 may be removed so that stop member91 forms a positive mechanical stop for screw 95 and arm 33.

One end of a counterweight arm 100 is pivotally mounted on pivot arm 33,and a counterweight 101 is mounted-on the free end of arm 100. A stop103 projects inwardly from counterweight arm 100 and is adapted tocontact pivot arm 33 in the rearward position of arm 100 shown in FIGS.1 and 2 so as to counterbalance the weight of head 51 to make the dop 67feel light and easy to handle by the operator.

counterweight 101 may be moved to its forward position by pushingcounterweight 101 and counterweight arm 100 forwardly about its pivotuntil stop 103 again engages pivot arm 33 at a position closer to head51. ln this forward position, the weight of counterweight the gem 71 isheld against lapping table 15 to grind the desired number and positionof girdle facets. Block 41 is called a girdle block because the head 51is inserted into block 41 when the girdle facets are being ground, andpivot block 29 is vertically positioned so that pin 37 is in about thesame horizontal plane as lapping table 15. The facets around the sidesof a gem are called girdle facets, the facets above the girdle facetsare crown facets, the facets below the girdle facets are pavilionfacets, and the large flat facet above the crown facets is the table.

After the girdle facets have been ground, head 51 and dop 67 are removedfrom girdle block 41 as a unit andare mounted on shaft 53 on the forwardend of pivot arm 33. Accordingly, since there has been no relativemovement between dop 67 and head 51, the pavilion facets may be groundin perfect alignment with the girdle facets. During the grindingoperation, the operator may lift a dop and head away from lapping table15 for visual inspection of the stone or gem 71 by rotating dop 67, head51, and pivot arm 33 around shaft or pin 37.

Regardless of the position of arm 33 the protractor 61 is alwaysmaintained in the same position relative to the vertical and to theplane of the lap table, because rotation of arm 33 around pin 37 causesrotation of block pulley 31 which moves cable 59 to rotate head pulley57 to hold protractor 61 in the same position relative to lapping table15.

During the grinding of the facets, pivot arm 33 moves downwardly, asdoes stop adjustment screw 97 which moves against sensor 95 thatprovides a signal which is translated by its electrical circuit toactuate a visual indicator with a pointer that moves in response to theprogress of the grinding. When the pointer reaches a I certain markingon the visual indicator, the grinding of the facet is finished. Thisvisual indicator makes it easy for the operator to grind all facets ofthe same course to the same degree so that they are identical.

It is to be noted that pivot block 29 rotates freely about'vertical post21 permitting pivot arm 33 and the gem 71 to sweep across the lappingtable 15. Post 21- justment of the facet-to-girdle angle.

101 bears downwardly against dop 67 and helps to hold the gem 71 againstlapping table 15. This forward position of counterweight 101 is usefulin polishing the gem 71 automatically without requiring the hand orattention of the operator.

In operation, a preformed stone or g'em 71, preformed in that it hasbeen ground to its approximate final shape, is adhesively attached tothe dop 67 with wax in the usual fashion. Head shaft 53 is inserted intohole 105 in girdle block 41 and is held in place by tightening set screw107.1ndex plate 72 is rotated to various notches and held in place byindex plate clamp 75 and Head 51- may be locked in a position with dop67 vertical with respect to lapping table 15 so that the table may becut on gem 71 without using an adaptor block and without removing thedop 67 from head 51. The electical circuit for the faceting micrometeris as shown in FIG. 7 and provides a nonlinear output so that the meterreading gives a highly accurate indication of when the facet has beenground to the proper depth. lnput lines 111, 112 receive 1 15 volts ACwhich are impressed across the primary of a transformer l 13. A switch115 is provided in line 111. The output of transformer 1 13 is 12 voltsAC, and this voltage is rectifiedby diode 133, limited by Zener diode135, and filtered by capacitor 1 17. Unijunction transistor 1 19 andresistors 139, 143 and 145 and capacitor 141 constitute an oscillatorthe output of which is in the audio range and is amplified by adirect-coupled transistor 121. The collector output is applied to thesensor 95, a variable capacitor having a fixed plate 95b and a pivotedplate 95a which transmit a signal proportional to capacity to a receivertransistor 123. The output from transistor 123 is clamped by a germaniumdiode 125, thus producing a direct current through meter 127 which isproportional to the output from sensor 95. Meter 127 is zeroed by asmall off-set voltage through the resistor network that includes 3.3 kohm resistor 129 and 470 ohm resistor 131.

The capacitor sensor 95 comprises pivoted plate 95a and fixed plate 95b,and pivoted plate 95a is driven toward plate 95b as the grinding actionon the stone 71 proceeds, producing a non-linear output approximatelyaccording to the square root law. Accordingly, sensitivity of the meterreading increases as the cutting or grinding proceeds. This highsensitivity permits great accuracy as to repeatability of facet depth,since the cutting is stopped when the needle of the meter indicates acertain meter reading.

In practice, satisfactory results have been obtained where transformer113 is a 115/12 volt transformer, rectifier 133 is a 12 volt transistordiode, Zener diode 135 has a reverse breakdown voltage of 12 volts,resistor 137 is 47 ohms, capacitor 117 is a 250 microfarad voltcapacitor, resistor 139 is 3.9 k ohms, capacitor 141 is 0.1 microfarads,resistor 143 is 500 ohms, resistor 145 is 47 ohms, capacitor 147 is 0.02microfarads, resistor 149 is 500 ohms, capacitor 151 is a 1 microfarad 6volt capacitor, resistor 153 is 100 ohms, capacitor 155 is a 5microfarad 6 volt capacitor, resistor 157 is a 1 megohm resistor,resistor 159 is 1 k ohms, resistor 161 is 100 ohms, capacitor 163 is a 5microfarad 6 volt capacitor, and capacitor 165 is a l microfarad 50 voltcapacitor.

The operation of the electronic micrometer is as follows. A dop stone 71rests on the lap 15. The head 51 is locked on the pivot arm 33 so thatthe stone 71 is addressed to the lap or lapping table 15 at a desiredangle, for example 45, as indicated by the protractor 61. Stopadjustment screw 97 is mounted on rod 99 extending from pivot arm 33 andas the pivot arm 33 moves downwardly as the cutting of the stone 71progresses, the stop adjustment screw 97 contacts the upper plate 95a ofsensor 95 which is lightly spring loaded and may be compressed aboutone-tenth of an inch before it stops the downward movement of pivot arm33. As the pivot arm 33 moves downwardly, upper plate 95a movesdownwardly proportionately and sends a signal to the amplifier. Althoughthe movement of sensor plate 95a is linear with respect to movement ofthe pivot arm 33, the output from sensor 95 is non-linear, increasingapproximately according to the square of the distance travelled by upperplate 95a. Thus as the cutting or grinding of the facet proceeds, thesensor 95 becomes increasingly sensitive to the movement of the stone asthe stone material is ground away. At the high end of the meter scale,movement of the stone 71 is about one-thousandth of an inch per meterdivision. This high sensitivity enables the cutter to cut or grind aseries of facets, as required in a round brilliant, for example, byadvancing the index plate '9'5a and observing the meter. It is notnecessary to examine the stone 71 after each facet is cut, you simplyout each facet to the same meter reading.

The pivot block 51 is important to the easy use of the electronicmicrometer because stop screw 97 may be adjusted to contact sensor 95regardless of the faceting angle or the size of the stone 71.

Gem faceter 11 is adapted for automatic operation in that an operatorcan set the faceter to grind with the dop stone 72 on lapping table 15and walk away and the faceter grinds until pivot arm 33 brings stopadjustment screw 97 into contact with a mechanical or electrical stopmechanism. The head and arm mechanism of gem faceter 11 are balanced soas to grind facets automatically, which is something that cannot be donewith a conventional high-post gem faceter. An operator can handle anumber of gem faceters 11 at the same time.

An angle compensator 167 is provided for adjusting or rotating indexplate 72 and dop 67 relative to head 51 for an angle less than the anglebetween notches 73 on index plate 72 without moving head 51 or looseninghead clamp knob 55. For example, the operator may wish to rotate indexplate 72 a quarter degree or a half degree when it is ascertained byvisual inspection that facets on stone 71 are not exactly aligned aftertransfer dopping, an operation wherein the stone 71 is transferred toanother dop. The table of stone 71 is adhesively attached to dop 67during the grinding of the girdle and pavilion facets. Then stone 71 istransferred to another dop and the pavilion is adhesively adhered to thedop so that the table facet of stone 71 may be ground. During thistransfer of the stone 71 from one dop to another, a small misalignmentmay occur between the position of stone 71 with the'first dop and thesecond dop.

Angle compensator 167 includes an adjustment block 169 which ispivotally mounted on head 51 so as to be rotatable about the center axisof the dop 67, a rotary adjustment screw 171 which is threaded throughblock 169 and is adapted to abut against the broadened base of pointer65 fixedly mounted on head 51, and a spring 173 with one end mounted onhead 51 and its free end bearing against the upper portion of adjustmentblock 169, above its pivot, to urge block 169 toward the head of rotaryadjustment screw 171 Finger 77 is pivotally mounted at one end in thetop of block 169, and the other end of finger 77 is positioned in avertical notch in a front plate 177 having a rearwardly extending flange179 through which is threaded locking screw 79 having a shoulder whichbears down on finger 77 to hold it in notches 73.

In operation of angle compensator 167, block 169, finger 77, lockingscrew 79, front plate 1 l7 and flange 179, index plate 72, dop 67, andstone 71, all move as a unit and rotate about the longitudinal axis ofdop 67,

moving relative to head 51. While this rotary adjust- .a head pivotallymounted on the other end of the.

pivot arm, a dop rotatably mounted in said head,

index plate means fixedly mounted on said dop for rotatively positioningsaid dop to grind desired facets on a gem held by said dop, index platelocking means for holding the index plate means and dop indesiredpositions relative to said head for grinding the desired facets, alapping table adapted to be contacted by the gem mounted on said dop,and means forindicatingthe angular position of the dop relative to thevertical. 2. The gem faceter of claim '1 including adjustable stop meansfor limiting the movement of said head around a horizontally positionedpivot.

' 3. The gem faceter of claim 2 including micrometer sensing meansmounted on said stop means for sensing the degree of movement of a gemmounted on said dop.

4. The gem faceter of claim.3 including means for translating saiddegree of movement sensed by the sensing means into an electronicsignal, and visual means adapted to receive the electronic signalandvisually indicate its value,

whereby the depth of the facet may be detected and duplicated with greatprecision.

S. The gem faceter of claim '1,

said index plate means including an indicator plate in the form of adisk attached to the dop,

and a number of notches formed in the perimeter of the index plate,

said notches being programmed so as to grind facetsof desired number andposition.

v 6. The faceter of claim I,

including protractor means which indicates the angle of the dop relativeto the vertical.

7. The gem faceter of claim 6,

said protractor means including a pulley fixedly mounted onsaid pivotblock, a head pulley freely mounted on a shaft extending between thehead and the pivot 'arm,

a protractor with angle indicating markings fixedly mounted on the headpulley,

a pointer fixedly mounted onthe head and adapted to point to theprotractor markings to indicate the angle between the dop andthevertical,

and a .cable trained around said pulleys whereby movement of the dop andpivot arm about the pivot block pivot pin causes relative movement ofthe protractor to maintain its attitude in space,

whereby the position of the pointer against the protractor markingscontinuously indicates the angle between the dop and the vertical. I

8. The gem faceterv of claim 1 including counterweight means mounted onthe pivot arm and having a first positionfor making the head and doplighter and easier to handle,

stop means for holding the pivot arm in said first position, a

a second position wherein its weight bears against the gem to hold it incontact with the lapping table to assist in polishing the gemautomatically,

Y and stop means for holding the pivot arm in said second position. I

9. The gem faceter of claim 1 including angle compensator means foradjusting the rotative position of said index plate means withoutunlocking said index plate locking means.

10. The gem faceter of claim 1 wherein said angle compensator meansincludes an adjustment block pivotally mounted on said head andconnected to said index plate means,

adjustment screw means threaded through said adjustment block forrotating said adjustment block and index plate means in one direction,

and spring means pressing against said adjustment block and urgingrotation thereof in the opposite direction.

1. A gem faceter comprising a base, a vertical post mounted in saidbase, means for moving said post to various vertical positions andlocking it in place, a pivot block mounted on said post and movablevertically therewith, a pivot arm having one end pivotally mounted tothe pivot block, a head pivotally mounted on the other end of the pivotarm, a dop rotatably mounted in said head, index plate means fixedlymounted on said dop for rotatively positioning said dop to grind desiredfacets on a gem held by said dop, index plate locking means for holdingthe index plate means and dop in desired positions relative to said headfor grinding the desired facets, a lapping table adapted to be contactedby the gem mounted on said dop, and means for indicating the angularposition of the dop relative to the vertical.
 2. The gem faceter ofclaim 1 including adjustable stop means for limiting the movement ofsaid head around a horizontally positioned pivot.
 3. The gem faceter ofclaim 2 including micrometer sensing means mounted on said stop meansfor sensing the degree of movement of a gem mounted on said dop.
 4. Thegem faceter of claim 3 including means for translating said degree ofmovement sensed by the sensing means into an electronic signal, andvisual means adapted to receive the electronic signal and visuallyindicate its value, whereby the depth of the facet may be detected andduplicated with great precision.
 5. The gem faceter of claim 1, saidindex plate means including an indicator plate in the form of a diskattached to the dop, and a number of notches formed in the perimeter ofthe index plate, said notches being programmed so as to grind facets ofdesired number and position.
 6. The faceter of claim 1, includingprotractor means which indicates the angle of the dop relative to thevertical.
 7. The gem faceter of claim 6, said protractor means includinga pulley fixedly mounted on said pivot block, a head pulley freelymounted on a shaft extending between the head and the pivot arm, aprotractor with angle indicating markings fixedly mounted on the headpulley, a pointer fixedly mounted on the head and adapted to point tothe protractor markings to indicate the angle between the dop and thevertical, and a cable trained around said pulleys whereby movement ofthe dop and pivot arm about the pivot block pivot pin causes relativemovement of the protractor to maintain its attitude in space, wherebythe position of the pointer against the protractor markings continuouslyindicates the angle between the dop and the vertical.
 8. The gem faceterof claim 1 including counterweight means mounted on the pivot arm andhaving a first position for making the head and dop lighter and easierto handle, stop means for holding the pivot arm in said first position,a second position wherein its weight bears against the gem to hold it incontact with the lapping table to assist in polishing the gemautomatically, and stop means for holding the pivot arm in said secondposition.
 9. The gem faceter of claim 1 including angle compensatormeans for adjusting the rotative position of said index plate meanswithout unlocking said index plate locking means.
 10. The gem faceter ofclaim 1 wherein said angle compensator means includes an adjustmentblock pivotally mounted on said head and connected to said index platemeans, adjustment screw means threaded through said adjustment block forrotating said adjustment block and index plate means in one direction,and spring means pressing against said adjustment block and urgingrotation thereof in the opposite direction.